Encoding a first modulation type with a first spectral efficiency into a second modulation type capable of having a second spectral efficiency

ABSTRACT

In a first embodiment, a method and apparatus for encoding a first spectral efficiency into a second spectral efficiency; wherein the second spectral efficiency has a higher order than the first spectral efficiency. In a second embodiment, a method and apparatus for achieving at least two spectral efficiencies using a single type of modulation.

RELATED APPLICATIONS AND PRIORITY CLAIM

This application is a Continuation claiming the benefit of U.S. patentapplication Ser. No. 16/858,869 filed Apr. 27, 2020 entitled “ENCODING AFIRST MODULATION TYPE WITH A FIRST SPECTRAL EFFICIENCY INTO A SECONDMODULATION TYPE CAPABLE OF HAVING A SECOND SPECTRAL EFFICIENCY,” whichis a Continuation claiming the benefit of U.S. patent application Ser.No. 16/102,376 filed Aug. 13, 2018 entitled “ENCODING A FIRST MODULATIONTYPE WITH A FIRST SPECTRAL EFFICIENCY INTO A SECOND MODULATION TYPECAPABLE OF HAVING A SECOND SPECTRAL EFFICIENCY,” now issued as U.S. Pat.No. 10,637,578 on Apr. 28, 2020, which claims the benefit U.S.Provisional Patent Application Ser. No. 62/546,894, filed Aug. 17, 2017entitled “ENCODING A FIRST MODULATION TYPE WITH A FIRST SPECTRALEFFICIENCY INTO A SECOND MODULATION TYPE CAPABLE OF HAVING A SECONDSPECTRAL EFFICIENCY,” all of which are hereby incorporated herein byreference in their entireties.

BACKGROUND

Optical transmission of information over a fiber optic cable oftenencodes the information on a light wave.

SUMMARY

In a first embodiment, a method and apparatus for encoding a firstspectral efficiency into a second spectral efficiency; wherein thesecond spectral efficiency has a higher order than the first spectralefficiency. In a second embodiment, a method and apparatus for achievingat least two spectral efficiencies using a single type of modulation.

BRIEF DESCRIPTION OF THE FIGURES

Various aspects and embodiments of the application will be describedwith reference to the following example embodiments. It should beappreciated that the figures are not necessarily drawn to scale.

FIG. 1a is a simplified illustration of a BPSK constellation, inaccordance with an embodiment of the present disclosure;

FIG. 1b is a simplified illustration of a QPSK constellation, inaccordance with an embodiment of the present disclosure;

FIG. 1c is a simplified illustration of a 16-QAM constellation, inaccordance with an embodiment of the present disclosure;

FIG. 2a is a simplified illustration of a BPSK constellation with poweron the I component and no power on the Q component, in accordance withan embodiment of the present disclosure;

FIG. 2b is a simplified illustration of a BPSK constellation with poweron the Q component and no power on the I component, in accordance withan embodiment of the present disclosure;

FIG. 2c is a simplified illustration of a BPSK constellation with equalpower on the I component and Q component, in accordance with anembodiment of the present disclosure;

FIG. 2d is a simplified illustration of a BPSK constellation with powerdistributed unequally between the I component and Q component, inaccordance with an embodiment of the present disclosure;

FIG. 3a is a simplified illustration of changing of a BPSK signal in aP-QPSK signal, in accordance with an embodiment of the presentdisclosure;

FIG. 3b is a simplified method of changing a BPSK signal into a P-QPSKsignal, in accordance with an embodiment of the present disclosure;

FIG. 3c is a simplified illustration of changing of a P-QPSK signal intoa BPSK signal, in accordance with an embodiment of the presentdisclosure;

FIG. 3d is a simplified method of demodulating a P-QPSK signal into aBPSK signal, in accordance with an embodiment of the present disclosure;

FIG. 4 is a simplified illustration of a constellation that has a BPSKsignal encoded onto a QPSK constellation, in accordance with anembodiment of the present disclosure;

FIG. 5 is a simplified illustration of a set partitioned mapping for 16QAM, in accordance with an embodiment of the present disclosure;

FIG. 6 is an alternative simplified illustration of a set partitionedmapping for 16 QAM, in accordance with an embodiment of the presentdisclosure;

FIG. 7a is a simplified illustration of changing of encoding a firstspectral efficiency into a second spectral efficiency, in accordancewith an embodiment of the present disclosure;

FIG. 7b is a simplified method for changing a first spectral efficiencyinto a second spectral efficiency, in accordance with an embodiment ofthe present disclosure;

FIG. 7c is a simplified illustration of changing a second spectralefficiency to a first spectral efficiency, in accordance with anembodiment of the present disclosure;

FIG. 7d is a simplified method for changing a second spectral efficiencyto a first spectral efficiency, in accordance with an embodiment of thepresent disclosure; and

FIG. 8 is a simplified illustration of a geometrically shaped 32-QAMmodulation format, in accordance with an embodiment of the presentdisclosure.

SPECIFICATION

Often, a transmitter may use a modulation scheme to transmit data usinga signal to a receiver. Conventional modulation schemes associate databits with symbols. Quadrature amplitude modulation (QAM) is one exampletype of a typical type of modulation scheme and is commonly used in manycommunication systems including fiber optical and digital radiocommunications. Generally, the number of different symbols in amodulation format determines the order of a digital communicationscheme. Conventionally, higher order modulation formats enable carryingmore bits of information or parity bits per symbol. Usually, byselecting a higher order format of QAM, the data rate of a link can beincreased.

Conventionally, a QAM scheme may be associated with a constellationdiagram having M points arranged in a two-dimensional plane. Usually,the M points represent the M possible symbols to which data bits may bemapped, where M is an integer. For example, an 8QAM scheme may beassociated with a constellation diagram having 8 points arranged in atwo-dimensional plane representing 8 possible symbols to which data bitsmay be mapped. As another example, in conventional 16QAM, data bits aremapped to 16 different symbols. Generally, each particular one of the Mpoints may be associated with a label indicating the bit sequence mappedto the symbol represented by the particular one point. For example, aparticular one of the 8 points in a constellation diagram for 8 QAM maybe associated with a label (e.g., “010”) indicating that data bits “010”are mapped to the symbol represented by the particular one point.Conventional examples of QAM schemes include 8QAM, 16QAM, 32QAM, 64QAM,and 256QAM schemes.

Typically, high order optical quadrature amplitude modulation “QAM”schemes are commonly utilized in fiber optical networks to handleincreasing traffic. Generally, because the QAM signal order is limitedby transmission length, it is important that the optical transmittersand receivers (transceivers) can be configured to operate with severalQAM signal orders to support trade-offs of transmission distance andcapacity. Typically, QAM signal order also affects the spectralefficiency of the system. Usually, a higher order may mean higherspectral efficiency because more data can be transmitted with eachchannel use while occupying the same amount of spectral width.Conventionally, the greater the distance the harder it is to support ahigher QAM signal due to interference with the signal.

Conventionally, optical transmitters and receivers employ automaticcontrollers to stabilize e.g. modulator bias voltages, driver signalamplitudes and received signal amplitudes at the desired operatingpoints. Usually, most of the control algorithms require data on I and Qchannels to be uncorrelated and of equal power. Generally, I and Qchannels carry uncorrelated data for most modulation formats like QPSKand 16-QAM. Typically, BPSK can be an exception where all the signalpower may be aligned to the I-component only, leaving no power on theQ-component.

In many embodiments, modulation formats based on higher order modulationmay be modified to operate at lower spectral efficiencies. In certainembodiments, spectral efficiency of BPSK may be achieved with a signalthat looks like QPSK to the optical transmitter and receiver. In certainembodiments, a BPSK signal that appears as QPSK signal may enable anautomatic control algorithm designed for higher order QAM modulationformats to be used on the BPSK signal encoded as the QPSK signal. Insome embodiments, use of a modulation format where a BPSK signal appearsas a QPSK signal may enable the use of receiver algorithms that aredesigned for QPSK such as CMA equalizers. In other embodiments, highermodulation formats may also be used to transmit data for lowermodulation formats or lower spectral efficiencies, providing the lowermodulation format.

In many embodiments, using higher modulation formats to transmit data atspectral efficiencies of lower modulation formats may enable transitionof spectral efficiencies or the information rate without changing amodulation format. In a particular embodiment, QPSK may be used totransmit the information with 1 bit/symbol as in BPSK. In mostembodiments, modulation of order N may be used to achieve spectralefficiencies less than N using this scheme. In certain embodimentsherein, this may be called Pseudo-M-QAM (P-M-QAM) where M=2{circumflexover ( )}N.

In most embodiments, Pseudo-M-QAM schemes may be useful for transitionof spectral efficiencies without changing the modulation format. In anembodiment, a transceiver may be initially configured for 64-QAMoperation. In this embodiment, during operation the distance and fibercharacteristics may change due to dynamic channel reconfiguration, whichmay require the transceiver to change the spectral efficiency. Incertain embodiments, one way to change a spectral efficiency may be tomodify the modulation order. In some embodiments, modifying themodulation order may disrupt automatic control loops causing glitches onthe transmission. In many embodiments, a better transition with littleor no impact of a transition between modulation modes to a differentspectral efficient may be achieved using P-M-QAM modulation.

In still other embodiments, analog control loops at the receive side maybenefit from circularly symmetric constellations, like automatic gaincontrol (AGC) in the receiver. In certain embodiments, if aconstellation is asymmetric, as in the case of BPSK, then specialcoupling between an I and Q channel may need to be taken into account inorder to ensure proper AGC functionality even at very low frequencyoffset between the carrier and the local oscillator, which may result ina slowly rotating constellation at the receiver.

In some embodiments, constant modulus algorithm (CMA) may be used at areceive side in communication systems for equalization of variousimpairments including inter symbol interference and polarization modedispersion (PMD). In many embodiments, CMA may fail to converge withBPSK because a pre-requisite of CMA may not be satisfied. In certainembodiments, CMA may require a constellation to be circularly symmetric,i.e. E(a²)=0, while for BPSK E(a²)=1. In some embodiments, variousalgorithms may be used for the equalization of BPSK signals, howevermany of these algorithms include extra operations that require morepower and area on the ASIC, and increase the design and verificationtime.

In certain embodiments, it may be beneficial to encode a BPSK typesignal onto a signal with higher spectral efficiency to make enable useof CMA to correct for various impairments. In many embodiments, it maybe beneficial to encode a spectral efficiency that is not circularlysymmetric into a spectral efficiency that is circularly symmetric. Inmany embodiments, one or more of the techniques described herein may beused to achieve different spectral efficiencies using a single type ofmodulation. In a particular embodiment, it may be possible to use 16 QAMmodulation to achieve spectral efficiencies between 1 and 4 bits/symbol.In many embodiments, this may be achieved using a set partitionedmapping. In most embodiments, PRBS as used herein may stand for pseudorandom bits. In many embodiments herein, a PRBS generator may refer to apseudo random bit generator.

In some embodiments, in P-M-QAM modulation k PRBS bits may be generatedfor each group of n data bits where M=2{circumflex over ( )}(k+n). Incertain embodiments, spectral efficiency may be n bits/symbol. In manyembodiments, PRBS bits may be used to select a subset in the setpartitioned mapping. In some embodiments, data bits may be used toselect one of the constellation points inside the set. In certainembodiments, selection may allow maximum Euclidian distance between thesymbols for a given set of PRBS bits. In certain embodiments, to achievetwo bits/symbol with 16QAM modulation, it may be possible to generatetwo PRBS bits and couple them with a group of two data bits. In someembodiments, data bits may be used to select one of the constellationpoints in the subset. In certain embodiments, the PRBS bits are 00 thenthe left most subset may be selected. In some embodiments, two data bitsmay select one of the constellation points in the subset. In mostembodiments, by using known information for a portion of the encodedbits in a QAM modulation scheme, the distance between constellationpoints may be increased which may make it easier to determine what datawas encoded at a transmitter.

In some embodiments, a bit generator may be used to insert extrainformation into a transmission to encode a lower order type signal intoa higher order type signal. In most embodiments a transmitter andreceiver may have the same type of bit generator so the receiver maydecode the additional information out of a signal. In some embodimentsherein, a bit generator may be referred to as a PRBS generator. In mostembodiments, PRBS may refer to a pseudo random bit sequence.

In certain embodiments, a transmitter and a receiver may synchronizebits generated by a bit generator at the receiver and a bit generator ata transmitter. In some embodiments, one or more alignment words may beused to synchronize a bit generator at a transmitter and a bit generatorat a receiver. In most embodiments, an alignment word is a set of bitsor patterns that both an encoder and a decoder know. In manyembodiments, an alignment word may be referred to herein as a framealignment word.

In some embodiments, various methods may be used to achieve demodulationfor P-QPSK symbols. In a particular embodiment, the following may beapplied:

-   -   rotate P-QPSK symbols +45 degree if PRBS bit is 0 to end up on        I-component axis    -   rotate P-QPSK symbols −45 degree if PRBS bit is 1 to end up on        I-component axis        In certain embodiments, applying at least some of the methods        herein may generate a regular BPSK symbol. In many embodiments,        methods designed to demodulate or generate soft metric for BPSK        symbols may be utilized.

Refer now to the example embodiment of FIGS. 1a, 1b, and 1c . FIGS. 1a,1b, and 1c show examples embodiments of QAM constellations, according toaspects of the current disclosure. In the example embodiment of FIG. 1a, QAM signal order, or number of points in the constellation, is two forBPSK (binary phase shift keying). In the example embodiment of FIG. 1b ,signal order, or number of points in the constellation, is four for QPSK(quadrature phase shift keying). In the example embodiment of FIG. 1b ,signal order, or number of points in the constellation, is 16 for 16-QAM(16-quadrature amplitude modulation). In the example embodiment of FIGS.1a, 1b, and 1c , the number of bits transmitted per symbol is one, twoand four for BPSK, QPSK and 16-QAM respectively. In these exampleembodiments, the QAM signal can be generated as a superposition of tworeal-valued signals, called Inphase (I) and Quadrature (Q) component. Aswell, as used herein, the constellations, such as those of FIG. 1, mayalso be called a modulation type.

Refer now to the example embodiments of FIGS. 2a, 2b, and 2c , whichillustrate BPSK constellations in different orientations. In the exampleembodiment of FIG. 2a , all power is on the I-component, with no poweron the Q-component. In the example embodiment of FIG. 2b , all power ison the Q-component, with no power on the I-component. In the exampleembodiment of FIG. 2c power is equal on I- and Q-component, but bothcomponents are maximally correlated. In the example embodiment of FIG.2d , this represents a case in between that of FIG. 2a and FIG. 2 c.

In many embodiments, the ratio of signal power in the I-component versussignal power in the Q-component may depend on the orientation of theconstellation points in the case of BPSK modulation. In mostembodiments, this may be called a circularly asymmetric constellation.For example, in the example embodiments of FIGS. 1b and 1c the QPSK and16-QAM constellations are circularly symmetric constellations. In theseparticular embodiments, the average signal power on the I-component isalways equal to the power on the Q-component for arbitrary angles ofrotation of those constellations.

In some embodiments, correlated data (as in the example embodiments inFIG. 2c or in FIG. 2d ) may be addressed by employing BPSK-specificoptical components—these do not support other QAM signal orders. Inother embodiments, this may be addressed by designing specialmulti-format control schemes that increase hardware complexity and oftenresult in inferior performance.

Refer now to the example embodiments of FIGS. 3a and 3b , whichillustrates modulation of sample P-QPSK symbols. In the exampleembodiment of FIG. 3a , pseudo random bits generated by PRBS generator320 (step 340) are coupled with information bits 310 (step 345). Eachinformation bit of information bits 310 and a corresponding coupled bitfrom PRBS generator 320 are mapped to QPSK symbols by QPSK modulator 330(step 350).

Refer now to the example embodiments of FIGS. 3c and 3d , whichillustrate demodulation of sample P-QPSK symbols. PRBS generator 355generates a bit, which for received time period, matches a bit generatedat a transmitter (step 360). QPSK demodulator demodulates received QPSKsignal 355 and removes a non-information bit generated by PRBS generator355 to produce an output information bit as encoded at a transmitter(step 365).

In a particular embodiment of the example embodiments of FIGS. 3a, 3b,3c, and 3d PRBS generator 320 at a transmitter may generate the samebits as PRBS generator 355 at a receiver. In the particular embodiment,the PRBS generators at the transmitter and receiver may be synchronized.In this particular embodiment, alignment word (AW) may be utilized forframe synchronization purposes (i.e. synchronization). In manyembodiments, by looking at a transmission from an encoder to a decoder,a AW may enable a decoder to know when a PRBS generator has startedgenerating additional bits. In the example embodiments of FIGS. 3a, 3b,3c , and 3 d, these AWs may also be used here to synchronize the PRBSgenerators. In many embodiments, PRBS generators may be initialized to asame state at both a transmitter and a receiver after a AW to achievesynchronization.

Refer now to the example embodiment of FIG. 4, which illustrates aconstellation encoding BPSK into QPSK. In the example embodiment of FIG.4, the first bit represents PRBS data and the second bit represents databits. In the example embodiment of FIG. 4, the Euclidian distance ismaximum between two symbols for a given PRBS bit. In the exampleembodiment of FIG. 4, this is due to using set partitioned mapping. Inthe example embodiment of FIG. 4, Gray mapping may not allow for this,causing inferior performance. Typically, Gray mapping is commonly usedwith regular QPSK modulation. In most embodiments, the currentdisclosure realizes that, such as in the example embodiments of FIGS.3a, 3b, 3c, and 3d , Gray mapping may be a bad choice for this scheme.In most embodiments, adjacent symbols may differ by only one bit in Graymapping. In many embodiments, this may mean that a symbol errorintroduced in channel causes only 1 bit of error at the demodulator.This is preferred in certain embodiments. In other embodiments, a goalmay be to achieve maximum Euclidian distance on the constellation pointsthat share the same PRBS bits. In embodiments where it is desired tomaximize Euclidian distance between the constellation points that sharethe same PRBS bits, set partitioned mapping may be used. In the exampleembodiments of FIGS. 3a, 3b, 3c, and 3d , a set partitioned mapping maybe set as given.

Refer now to the embodiment of FIG. 5, which illustrates a setpartitioned mapping for 16 QAM, according to an aspect of the currentdisclosure. As shown in the example embodiment of FIG. 5, a setpartitioning divides a signal set successively into smaller subsets withmaximally increasing smallest intra-set Euclidian distances denoted byd_(min) in FIG. 5. In the example embodiment of FIG. 5, each partitionis two-way. In the example embodiment of FIG. 5, the partition isrepeated 4 times in the figure. In the example embodiment of FIG. 5, thefinally obtained subset are labelled S0, S1, . . . S15. In the exampleembodiment of FIG. 5, the labeling of the branches indicates theposition of the subset. In the example embodiment of FIG. 5, thislabeling also shows how to map bits to symbols. In the exampleembodiment of FIG. 5, for example, data bits 0101 is denoted by circlesin the figure is mapped to constellation point labelled with subset S5.

For example, refer to the example embodiment of FIG. 6. In the exampleembodiments of FIG. 6, two PRBS bits may be used to select one of thesubsets denoted by the circles in the FIG. 6. In FIG. 6, once the knownPRBS bits are encoded out of the constellation, it is easier to decodethe remaining information as the minimum distance, d_(min) has increasethrough the use of the known encoded bits from the PRBS generator. Inthe example embodiment of FIG. 6, as the distance becomes greater, itbecomes easier to select the correct bit encoding.

FIGS. 7a, 7b, 7c, and 7d are example embodiments of the modulation anddemodulation for a pseudo modulation method, according to an embodimentsof the current disclosure. Refer now to the example embodiments of FIGS.7a and 7b , which illustrate modulation of sample P-QAM symbols. In theexample embodiment of 7 a, data bits 0 710-data bits n-1 715 areinputted into set partitioned mapping of order 730 (step 740). Pseudorandom bits are generated by PRBS generator 0 720 to PRBS generator k-1725 (step 735) and inputted into set partitioned mapping of order 730(step 740). Information bits are combined with PRBS generated bits byset partitioned mapping of order 730 and mapped to a signal (Step 745).In the example embodiment of FIG. 7a , PRBS generator 0 720 to PRBSgenerator k-1 725 represent the number of PRBS random generators toneeded to generate random bits to increase the spectral efficiency ofthe QAM signal.

Refer now to the example embodiments of FIGS. 7c and 7d , whichillustrate demodulation of sample P-QPSK symbols. PRBS generator 755 toPRBS generator k-1 760 generates PRBS bits (step 770), which forreceived time period, matches a bit generated at a transmitter.Demodulator 765 receives inputted PRBS generator 755 to PRBS generatork-1 760 PRBS Bits and receives input signal 750 (steps 772 and step776). Demodulator 765 demodulates input signal 750 and uses PRBS bits todecode information bits from demodulated input signal 750 (step 780). Inthe example embodiment of FIG. 7a , PRBS generator 755 to PRBS generatork-1 760 represent the number of PRBS random generators to needed togenerate random bits to match the random bits generated at a receiver toincrease the spectral efficiency of the QAM signal.

Consider the further example embodiments of FIGS. 8a, 8b, and 8c . Inthe example embodiments of FIG. 8a and FIG. 8b , the constellations arenot circularly symmetric. FIG. 8a represents data encoded in half of a16-QAM modulation format, similar to 8 QAM. FIG. 8b represents PRBS dataencoded in half of a 16-QAM format, similar for 8 QAM. FIG. 8a and FIG.8b , in isolation, may require stabilization to be circularly symmetric.In this embodiment, a combination of FIG. 8a and FIG. 8b yields FIG. 8c, which is circularly symmetric and Pseudo 16 QAM. In certainembodiments, aspects of techniques described herein, such as P-M-QAM,may be used to transmit 3 bits per symbol (SP-16-QAM, similar to 8 QAM)but the constellation of the signal may look like 16 QAM. In otherembodiments, the techniques of the current disclosure may be used toencode any spectral efficiency into a higher spectral efficiency with aknown bit

In many embodiments, the techniques described herein may be performedand/or stored on a computer, a processor, and other types of integratedcircuits or specially designed circuits. In some embodiments, thetechniques herein may be stored on firmware or computer readable mediumsuch as hard drives, RAM, and memory. In other embodiments, thetechniques herein may be part of a generalized computing device or aspecialized computing device. In certain embodiments, the currenttechniques may be used with fiber optic communication. In someembodiments, an encoder may be on a source side of a fiber opticcommunication system. In certain embodiments, a decoder may be on areceiving side of a fiber optic communication. In many embodiments, asource side of a fiber optic communication system may send a light waveto a receiving side. In certain embodiments, a fiber optic communicationsystem may use one or more of the techniques described herein.

In some embodiments, one or more of the embodiments described herein maybe stored on a computer readable medium. In certain embodiments, one ormore of the embodiments described herein may be embodied in a computerprogram product that may enable a processor to execute the embodiments.In many embodiments, one or more of the embodiments described herein maybe executed on at least a portion of a processor.

In most embodiments, a processor may be a physical or virtual processor.In other embodiments, a virtual processor may be spread across one ormore portions of one or more physical processors. In certainembodiments, one or more of the embodiments described herein may beembodied in hardware such as a Digital Signal Processor DSP. In certainembodiments, one or more of the embodiments herein may be executed on aDSP. One or more of the embodiments herein may be programed into a DSP.In other embodiments, one or more of the techniques herein may befabricated in a DSP. In some embodiments, a DSP may have one or moreprocessors and one or more memories. In certain embodiments, a DSP mayhave one or more computer readable storages. In many embodiments, a DSPmay be a custom designed ASIC chip. In other embodiments, one or more ofthe embodiments stored on a computer readable medium may be loaded intoa processor and executed.

Having thus described several aspects and embodiments of the technologyof this application, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those of ordinaryskill in the art. Such alterations, modifications, and improvements areintended to be within the spirit and scope of the technology describedin the application. It is, therefore, to be understood that theforegoing embodiments are presented by way of example only and that,within the scope of the appended claims and equivalents thereto,inventive embodiments may be practiced otherwise than as specificallydescribed. In addition, any combination of two or more features,systems, articles, materials, and/or methods described herein, if suchfeatures, systems, articles, materials, and/or methods are not mutuallyinconsistent, is included within the scope of the present disclosure.

Also, as described, some aspects may be embodied as one or more methods.The acts performed as part of the method may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. The transitional phrases “consisting of” and “consisting essentiallyof” shall be closed or semi-closed transitional phrases, respectively.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, orwithin ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value.

What is claimed is:
 1. An apparatus comprising: logic that enablesdecoding a signal enabled to be encoded with at least two spectralefficiencies in a single type of modulation; by enabling decoding of ahigher order modulation format mapped into an efficiency of a lowerorder modulation format by unmapping a first encoding signal order intoa second encoding signal order; wherein the first encoding signal orderuses a first modulation scheme; wherein the second encoding signal orderuses a second modulation scheme; and wherein the first modulation schemeuses fewer constellation points than the second modulation scheme. 2.The apparatus of claim 1 wherein the single type of modulation enablesswitching between the at least two encoding signal orders withoutdisrupting a control loop between a modulation module encoding datatransmitted using the single modulation type and a demodulation moduledecoding the data.
 3. The apparatus of claim 1 wherein the firstspectral efficiency is M-ary quadrature amplitude modulation (M-QAM) andwherein the second spectral efficiency is N-ary quadrature amplitudemodulation (N-QAM); further wherein N>M.
 4. The apparatus of claim 1wherein at least one of the two encoding signal orders is 8 quadratureamplitude modulation (QAM).
 5. The apparatus of claim 1 wherein at leastone of the two encoding signal orders is quadrature phase shift keying(QPSK).
 6. The apparatus of claim 1 wherein the logic further enables:generating a sequence of one or more known bits; and using the one ormore known bits for decoding the first modulation scheme into the secondmodulation.
 7. The apparatus of claim 6 wherein unique words is used tosynchronize the sequence of one or more known bits.
 8. The apparatus ofclaim 6 wherein the generating the sequence of known bits is done by oneor more pseudo random bit generators.
 9. The apparatus of claim 1wherein the mapping includes adding bits to a binary phase shift keying(BPSK) signal corresponding to a known sequence of bits to encode it toquadrature phase shift keying (QPSK) signal.
 10. A method to decode asingle modulation format enabled to contain two different orders ofmodulation; by enabling a decoding of modification of a higher ordermodulation format operating at an efficiency of a lower order modulationformat by: generating a sequence of one or more known bits; andunmapping a first encoded signal order from a second encoding signalorder; wherein the first encoded signal order uses a first modulationscheme; wherein the second encoded signal order uses a second modulationscheme; and wherein the first modulation scheme uses fewer constellationpoints than the second modulation scheme; wherein the one or more knownbits are used to decode the second modulation scheme into the firstmodulation.
 11. The method of claim 10, wherein a unique words is usedto synchronize the sequence of the one or more known bits.
 12. Themethod of claim 10 wherein the generating the sequence of known bits isdone by one or more pseudo random bit generators.
 13. The method ofclaim 10 wherein the first spectral efficiency is M-ary quadratureamplitude modulation (M-QAM) and wherein the second spectral efficiencyis N-ary quadrature amplitude modulation (N-QAM) further wherein N>M.14. The method of claim 10 wherein at least one of the two encodingsignal orders is 8 quadrature amplitude modulation (QAM).
 15. The methodof claim 10 wherein at least one of the two encoding signal orders isquadrature phase shift keying (QPSK).
 16. The method of claim 10 whereinthe mapping includes adding bits to a binary phase shift keying (BPSK)signal corresponding to a known sequence of bits to encode it toquadrature phase shift keying (QPSK) signal.
 17. An apparatuscomprising: logic that enables: decoding a signal order by unmapping afirst encoding signal order from a second encoding signal order torecover a higher order modulation format from a signal operating at anefficiency of a lower order modulation, wherein: the first encodingsignal order uses a first modulation scheme; the second encoding signalorder uses a second modulation scheme; and the first modulation schemeuses fewer constellation points than the second modulation scheme. 18.The apparatus of claim 17 wherein the mapping includes: generating asequence of one or more known bits; and encoding the generated sequenceof one or more bits and one or more data bits into the second encodingsignal order.
 19. The apparatus of claim 18 wherein the generation thesequence of known bits is done by one or more pseudo random bitgenerators.
 20. The apparatus of claim 17 wherein the first encodingsignal order is a binary phase shift keying (BPSK) signal and the secondencoding signal order is a quadrature phase shift keying (QPSK) signalto make the BPSK signal circularly symmetric.